The invention pertains to a coated article such as, for example, a coated cutting tool, a coated (solid) carbide drill and an end mill. The invention further pertains to a coated wear part such as, for example, valve body, punches and dies. More specifically, the invention pertains to a coated article such as a cutting tool or wear part that has a substrate and a coating scheme on the substrate. The coating scheme includes a coating layer of aluminum oxynitride deposited via chemical vapor deposition (CVD). The coating scheme further includes, in general, one or more other coating layers.
The invention also pertains to a method of making a coated article such as a cutting tool or wear part with an aluminum oxynitride coating layer. The method includes providing a substrate, and then depositing by chemical vapor deposition a coating scheme. The coating scheme includes at least one coating layer of aluminum oxynitride. The gaseous mixture includes the following gases: hydrogen, nitrogen, aluminum tri-chloride, carbon dioxide, hydrogen chloride, ammonia, and optionally carbon monoxide and/or argon.
Heretofore, in U.K. Patent Application GB 2 038 370 A to Fried Krupp, a cutting insert includes a coating scheme, which includes a metal oxynitride coating layer wherein the metal may be aluminum, titanium or zirconium. In one example, an indexable cutting insert of hard material was coated with a titanium carbide layer from a gaseous mixture of TiCl4 and CH4. Next, the titanium carbide coating layer was coated with a layer of Al2O2.8N0.2 with a nitrogen content equal to 4 atom %. The gaseous mixture comprised 50% H2, 46.6% N2, 0.4% NH4, 2% CO2 and 1% AlCl3. See page 1, lines 51-59.
In U.S. Pat. No. 4,950,558 to Sarin, a ceramic substrate has a coating scheme thereon. One of the coating layers comprises AlxOyNz, which is a compositionally graded coating. According to the Sarin patent (see Col. 5, lines 21-39), the aluminum oxynitride coating layer may be deposited by simultaneously carrying out the following reactions:AlCl3(g)+NH3(g)→AlN(s)+3HCl(g)  (1)2AlCl3(g)+CO2+3H2→Al2O3(s)+6HCl(g)  (2)In the examples, the aluminum oxynitride coating layer has a graded composition.
Even though earlier products included a CVD coating layer of aluminum oxynitride, there remains a need to provide a coated article such as a cutting tool or wear part, which has a coating scheme including an aluminum oxynitride coating layer, with improved performance properties. Such a coated cutting tool or wear part exhibits an aluminum oxynitride coating layer that has reduced tensile stress up to moderate compressive stress. The condition of reduced tensile stress or moderate compressive stress can be due to one or more of a lower thermal expansion property, a good thermal stability, or a high hardness.
It would be highly desirable to provide an improved coated article such as a coated cutting tool or coated wear part with a coating scheme that includes a coating layer of aluminum oxynitride wherein the cutting insert, as well as the wear part, has improved performance properties. These improved performance properties include increased wear resistance and increased thermal shock resistance.
Further, it would be highly desirable to provide a coated article such as a coated cutting tool or coated wear part, which has an aluminum oxynitride coating layer that exhibits a reduced tensile stress up to moderate compressive stress. By providing an aluminum oxynitride coating layer with a reduced tensile stress up to moderate compressive stress, the coated article exhibits a resistance to crack growth. In this kind of a coating, a condition of tensile stress supports crack growth and a condition of compressive stress avoids cracks and crack growth. Avoidance of cracks and crack growth is particularly advantageous in an application like interrupted cutting.
Further still, it would be highly desirable to provide a coated article such as a coated cutting tool or coated wear part, which has an aluminum oxynitride coating layer that has a lower thermal expansion property, i.e., no micro cracks seen at the surface of the coating. In a quantitative sense, this means zero cracks occurrence observed in the crater cross section of the coatings under 30× optical microscope. By providing an aluminum oxynitride coating layer with a lower thermal expansion property, the coated article eliminates the occurrence of thermal cracking which is beneficial in improving the thermal shock resistance of the cutting tools.
In addition, it would be highly desirable to provide a coated article such as a coated cutting insert or a coated wear part, which has an aluminum oxynitride coating layer that exhibits a good thermal stability, i.e., the coating still exists after heat treatment in a vacuum for 2 hours at 1200° C. This means no phase transformation detectable by X-ray diffraction. By providing an aluminum oxynitride coating layer with a good thermal stability, the coated article exhibits improved wear resistance.
Finally, it would be highly desirable to provide a coated article such as a coated cutting insert or a coated wear part, which has an aluminum oxynitride coating layer that exhibits a high hardness, i.e., a hardness value HV0.5 equal to at least about 2200 when measured per ISO 3878. By providing an aluminum oxynitride coating layer with a high hardness, the coated article exhibits improved wear resistance.